umm I can think of one way.. not sure if it would work or not... but... couldn't you use a "invisable" rod from the center of the lift head straight down and use it fo movment control? In the real world.. what you are trying to do uses bands inside that trun a pulley at each joint.. as the arm raises, the lower part of the band gets longer and the upper part of the band gets shorter , turning the head in relation to thearm... and keeping it level ... if that makes since? Ever seen a drafting table arm?... not sure how to make it work in carrara.. haven't explored much of that area yet... That's my best answer.. not sure if it helps...

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Hexagon, Carrara, Sculptris, and recently Sketchup.